1. Field of the Invention
The present invention is in the field of multiple disk refiners utilizing a large number of refiner disks some of which are rotatable relative to the others to provide for a very low intensity treatment of suspensions such as stock suspensions for the manufacture of paper. The invention involves the use of a rigid linkage to support and drive a large number of refining disks, permitting each to translate independently in the axial direction. The rigid linkage provides the required movement through the rotation at a pinned connection, thus eliminating large bending stress concentrations found in other support arrangements.
2. Description of the Prior Art
Paper stock, as it comes from beaters, digesters or other pulping machines is usually refined by passing the stock between grinding or refining surfaces which break up the fibrous materials and serve to create further separation and physical modification of the fibers.
A typical pulp refiner is disclosed in Thomas U.S. Pat. No. 3,371,873. This type of refiner includes a rotating disk which has annular refining surfaces on one or both sides. The disk refining surfaces are in confronting relation with non-rotating annular grinding surfaces and provide therebetween a refining zone in which the pulp is worked. The rotating disk and the refining surfaces are made of a substantially inflexible material such as cast iron or a hard stainless steel. The non-rotating grinding surfaces are made of similar material and are rigidly mounted so as to resist the torque created by the rapidly rotating disk and the pressure on the pulp material passing through the refining zone gap. Axial adjustment of the refining zone gaps is effected by axial shifting of the shaft on which the disk is mounted.
Rigid disk refiners of this type must be manufactured and assembled to close tolerances in order to set the refining zone gap width correctly. Because the loads supplied to the rigid disk are large during the refining process, a large and extremely rugged design is necessary so that the refining surface relationships do not change under load. This results in the rigid disk refiners being very costly due to the necessarily close tolerance machining, the need for large quantities of high-strength disk material, the bulky overall structure, the restrictive machine capacity, and the excessive assembly time requirements.
Substantial improvements in pulp refiners have been achieved with the development of the multiple disk refiner which operates at a low intensity. For example, in Matthew and Kirchner U.S. Pat. No. 4,531,681, issued July 30, 1985, entitled "Flexible Disk Refiner and Method" assigned to the same assignee as the present application, there is provided a refining apparatus including a plurality of radially extending, relatively rotatable and axially confronting refining surfaces between which the suspension must pass when being refined during relative rotation of the surfaces. Means are provided for effecting flow of the material radially between and across the surfaces. The drive means disclosed in that application involve the use of resiliently flexible support means which permit adjustment of the relatively rotating refining surfaces axially relative to each other depending upon the operating pressures, thereby achieving optimum material working results from the refining surfaces.
In a specific form of the invention disclosed in the aforementioned patent, there is provided a pulp refiner with ring-shaped refining surface plates of limited radial width which are mounted on interleaved margins of axially resiliently flexible or deflectable disk elements. Disk margins spaced from the interleaved margins on one set of the disk elements are secured to a rotor while the margins on another set of disks are secured non-rotatably or counterrotatably. The refining surface plates are made of a suitably hard, substantially rigid material. The disk elements, on the other hand, are made of axially resilient flexible material which strongly resists deformation of the radial and circumferential directions. Because of the manner in which the axially flexible disk elements are supported, there is an automatic axial self-adjustment of the refining surfaces during the pulp refining process for attaining pressure equalization and maintenance of substantially uniform gap widths between the rotating and non-rotating disk elements.
The multiple disk refiner represents a substantial improvement in the art of refining. It has been shown that with the use of a low-intensity, multiple disk refiner, pulp characteristics can be improved considerably over conventional refining techniques. Originally, such refiners were built using flexible diaphragms to restrain the refining disks and provide the torsional rigidity required to transmit rotational forces into the refining surfaces. The resiliency of the diaphragms permitted sufficient axial motion of the refiner disks such as required as each surface moves into close proximity to its adjacent neighbors as the refiner is loaded to its operational position.
It was found, however, that once a significant amount of wear occurred in the refining surface an additional amount of load was required to keep the surfaces within close proximity which reduced the ability of the refiner to provide low-intensity refining. Since the deflection occurring in a diaphragm is proportional to the cube of the load, it was determined that such a support was not optimum for a system subject to the amount of wear occurring in a commercial installation.
The type of prior art structures just described have met with some difficulties because of the various requirements which exist in industrial operation. While the diaphragm style supporting arrangement has proven to be effective in laboratory prototypes, further investigation has shown that this mechanism is not always completely effective when subjected to the expected axial deflection and torsional loads. Furthermore, the complicated mounting required provided considerable cost to the overall assembly.
One of the major difficulties involved the inability of the mechanism to withstand large torque reversals as sometimes occur accidentally during operation. This immediately contraindicated the use of many types of unidirectional arrangements as they would tend to buckle under such loads.